Is Derek Jeter just getting old? Are his troubles at the plate a natural decline in his skills? Have his attempts to tinker with his swing played a role? Or is he just in an early season slump?

Don Zomer has heard all the theories about why his greatest pupil from Kalamazoo Central High is struggling, but the retired coach wonders if the reason is something else. He knows Jeter is approaching a milestone that will put him in one of baseball’s most exclusive clubs.

It is practically blasphemy to suggest this. But is the pursuit of 3,000 hits already wearing on Jeter, who is batting .257 with four hits in his last 24 at-bats?

“I think it’s going to affect him,” Zomer said. “In fact, I think it may have already affected him. The way he’s in a slump — and I guess you can call it a slump — maybe that’s from the additional pressure.

“You wonder: Is he pressing to get this over? That would be something quite new.”

The great Jeter?

Pressing?

If you listen to one Hall of Famer who also chased 3,000 hits, it wouldn’t be the least bit surprising.

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The number, of course, sneaks up on no one. It is there for the world to see, on dozens of websites and newspapers, like the countdown to a rocket launch that moves very, very slow. Jeter has 2,979 hits. He likely will return from the Yankees’ current West Coast trip with a number approaching 2,990, which means full-throttle 3,000-mania will begin during the next homestand.

The additional media. The questions — he is already getting plenty of those — that come before every game. The live look-ins on national TV. The anticipation of the hit that will put him at the milestone, and if the whole thing drags out, the added attention with each at-bat.

Paul Molitor was already in the twilight of his career when Jeter broke into the majors, but two things impressed him about the young shortstop: He always came over to shake Molitor’s hand when they met on the diamond, and Jeter’s uncanny ability to treat every at-bat the exact same way, regardless of the circumstances.

That latter skill, Molitor said, “Is going to be tested now.”

He should know. Molitor is one of the 27 men in the 3,000-hit club, a milestone he reached on Sept. 16, 1996, with the Minnesota Twins. Just six players have joined the club since.

“As much as you prepare for it and try to stay as professional as you can, that gets harder as you get closer,” Molitor said in a phone interview last week. “In New York, it’s probably exponentially harder than I could have imagined, plus Derek is on a first-place team.”

Molitor was not. The Twins were out of the pennant race that year, so his quest was the only story line for the team as the season wound down. He had one advantage: Just four years earlier, he had watched teammate Robin Yount go through the same chase, and saw the toll it took on him.

“I could watch and see the focus and the demands, both from the media and on himself,” Molitor said. “Robin was the last guy in the world to play for numbers, and he was affected. He told me, ‘I wish I would have enjoyed it more.’ ”

So Molitor tried. He reached 2,998 hits on Sept. 14, with one more game left in a nine-game home stand. His family and friends gathered the next night at the Metrodome, hoping Molitor, a St. Paul, Minn. native, would deliver for the home crowd. He went 0-for-3, and the quest went off to Kansas City, Mo.

It was frustrating at the time, but looking back, Molitor sees it as a blessing. A much smaller group of family and friends — including Yount and Royals legend George Brett — were on hand at Kauffman Stadium when he became the only player to reach 3,000 hits with a triple.

Just 16,483 saw it happen.

“It’ll be a bit different for Derek,” Molitor said with a laugh.

But he believes the experience will be the same. It wasn’t until a few years later, when Molitor looked at the names in the club (and the names not in it) when he could appreciate the accomplishment. He is ninth all-time with 3,319 hits and thinks Jeter will pass him and reach the top five.

Still, when the Yankees shortstop is standing at the plate at 2,999, Molitor said, “That’ll be one of his biggest tests.”

“But I’d rather be up there at 2,999 hits than the seventh game of the World Series,” he said, “because one of those moments is about a whole lot of people, and the other is just about you.”

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You wonder if Jeter, who would rather talk about almost anything than his personal accomplishments, would prefer it the opposite way. This will be the agonizing part for Jeter, because just like the pursuit of Lou Gehrig’s team record two years ago, this is all about him.

“It’s not on my mind right now,” Jeter said last week when asked about 3,000 hits, adding that it wouldn’t be until he’s “one or two” away.

He won’t get that luxury. The focus has been on him for much of the past eight months already, first for his contentious, and unusually public, contract negotiations and then for his early-season struggles.

Now it’ll be on a single question: When? The Yankees have a 10-game homestand beginning on June 7, and then have six games on the road for interleague play in Chicago and Cincinnati.

If it drags on much past that, the questions will start again. Manager Joe Girardi said he “hopes it happens suddenly so he doesn’t have to talk about it,” perhaps remembering the 12 games it took Alex Rodriguez to get from 599 to 600 home runs last August.

When it does happen, his old baseball coach in Kalamazoo, Mich. will be watching. Don Zomer has seen Jeter rise to every challenge before, but never has he wondered if his famous pupil might be pressing before he does. This time? He’s not sure.

“I’m just hoping he takes the time to sit back and say, ‘I’ve really done something here,’ and celebrate a little bit,” Zomer said. “I think he will, because it’s been quite a journey.”